The present invention relates generally to a tubular product, and more particularly to a tubular product made of a fiber composite material.
The conventional tubular products, such as golf club, fishing rod, ski pole, etc., are generally made of a fiber composite material by the sheet rolling method or filament winding method. The sheet rolling method involves the use of a plurality of fiber sheets which are preimpregnated with resin and are rolled around a core shaft such that the fiber orientation of the fiber sheets forms a predetermined angle with the longitudinal direction of the core shaft. The fiber sheets and the core shaft are heated and then cooled. A tubular product is finally formed by withdrawing the core shaft. In light of some fibers being parallel to the longitudinal direction of the core shaft, the tubular product has a greater resistance to flexure. However, such a tubular product has a rigid spine that is formed at the junction of the ends of the fiber sheets. In addition, certain fiber sheets are wound irregularly. As a result, the tubular product so made is apt to have the uneven rigidity throughout the tubular product. The filament winding method involves the winding of the fiber tows on a core shaft in a spiral manner. The core shaft and the fiber tows are heated and then cooled to take shape. A tubular product is formed upon the withdrawal of the core shaft. The winding of the fiber tows on the core shaft is done with precision by a computer-aided technique. As a result, the tubular product has a uniformity in terms of physical property. However, the tubular product is relatively less resistant to flexure in view of the fibers forming with the longitudinal direction of the core shaft an angle ranging between 30 and 45 degrees. In other words, the fibers can not be so arranged that they are parallel to the longitudinal direction of the core shaft.
The primary objective of the present invention is to provide a tubular product which is greater in flexural strength than the tubular product made by the conventional filament winding method. The tubular product of the present invention has an appropriate weight and a tube wall of an appropriate thickness.
The tubular product of the present invention is formed of an inner layer and an outer layer. The inner layer is formed of a fiber tow by the filament winding method and is encircled entirely or partially by the outer layer which is formed of one or more of the fiber sheets by the sheet rolling method. The fiber orientation of the outer layer of fiber sheets can form a predetermined angle with the longitudinal direction of the tubular product. Preferably, the fiber orientation of at least one fiber sheet of the outer layer is parallel to the longitudinal direction of the tubular product.